weird results: octane matters?

[teoman]

The wffect of altitude is somewhat negated by the turbo (if your car has one).

[teoman]

Call me repetitive but a little bit of water injection could mimick higher octane fuel.

I would guesstimate a bit of water on your air filter.

[Isaac Zackary]

Originally Posted by redpoint5

Well, your Avalon has an OBDII port. It's a simple matter to connect a gauge and see what the timing advance is doing.

My Acura runs 40 degrees advance when running on about 90 or above octane, but on 87 does a bit less advance during freeway cruise. When I'm regularly driving the car, I can tell what octane is in it just by feel. It has more power when I load the engine heavy at low RPM.

I got the same MPG though regardless of octane.

I just got my Toyota Techstream today! It's a little glitchy though, but it's also telling me that I need Java 6 update 7 or newer, so I need to find that for the XP computer I'm running it on. I also need a way to charge the laptop via the 12V cigarette lighter plug. But I'll see what it's running at. It will be interesting to know.

Originally Posted by teoman

Call me repetitive but a little bit of water injection could mimick higher octane fuel.

I would guesstimate a bit of water on your air filter.

Ya, I've thought about water injection. But sub-freezing temperatures for a good part of the year kind of stop me from doing that. (It's 29°F right now, and I just drove home from work.)

Of course cool air also increases octane. In my air cooled bug the cold air made it run lean at high load (right around 14:1, via oxygen sensor and gauge). But I couldn't get it to ping, even going up from 5,000 to 10,000ft with my foot glued to the floor and the timing advance about 5 degrees more than normal and the compression ratio increased from 7.5 to 9.5. But I also was using ethanol free, which was also 91 octane.

[arcosine]

My Saturn get better mpg with premium because the timing retards with lower octane. The price per gallon and mpg work out to be about the same price per mile, though premium is peppier.

[19bonestock88]

Maybe I should try some 91 in my Ion? I didn’t think that normal “low performance” cars would benefit much...

[teoman]

How long does it take for the car to change the timing?

Also one could try pouring a bit of water on to the air filter to see if that helps detonation suppression. Obviously no going full throttle afterwards. But for low loads it should be fine.

[redpoint5]

All water in the filter would do is restrict the airflow. Don't think it would cool the air because air wouldn't flow through the wet portion. If it did flow through the wet portion, it would quickly become dry.

[teoman]

The air filters are usually over sized. Or siEd for full throttle.

It would obviously not be for the duration of a full trip. But if it were able to absorb 20 ml of water then it should increase the octane of 100ml of fuel which should be good for a couple of miles. Enough to see if there is a timing benefit. (In my opinion).

[Isaac Zackary]

Originally Posted by arcosine

My Saturn get better mpg with premium because the timing retards with lower octane... though premium is peppier.

Originally Posted by 19bonestock88

Maybe I should try some 91 in my Ion? I didn’t think that normal “low performance” cars would benefit much...

Most people wouldn't get much better fuel mileage from more octane because most people do most of their driving at low engine loads. At low engine loads you're restricting the air and causing less compression and therefore less heat. Also less fuel is used. It's basically the same reason you can use less octane at higher altitudes. When I had the digitally adjustable distributor on my air-cooled Beetle it was impossible to get the engine to ping at low cruising loads, regardless of timing. Basically advancing it up to a point caused power and efficiency to increase, and going over that it just caused that power and efficiency to decrease. Detonation protection is mainly needed at or near full throttle where you're compressing more air and burning more fuel, both of which cause more heat. And that heat can cause unburned fuel to want to detonate.

But if you're like me and have mostly steep mountain passes to climb or you pulse and glide (use high loads then let the car coast) then octane is going to make a bigger difference.

But in my opinion, whether you see a difference in fuel mileage or timing retarding at any load by changing the octane, you really should use the higher octane. What if the knock sensor malfunctions and your ECU doesn't detect that the fault and the engine starts pinging like crazy. Then next thing you know you could be out of an engine.

Originally Posted by redpoint5

All water in the filter would do is restrict the airflow. Don't think it would cool the air because air wouldn't flow through the wet portion. If it did flow through the wet portion, it would quickly become dry.

A restriction would decrease the need for octane.

[redpoint5]

Originally Posted by Isaac Zackary

A restriction would decrease the need for octane.

Of course; a restriction like the throttle, which is the best way to restrict airflow to the engine.